The one-time right-hand man of the Brazilian former president Luiz Inácio Lula da Silva has been found guilty of corruption over a cash-for-votes scheme that came to light seven years ago.

A majority of supreme court justices found José Dirceu guilty of "active corruption" by organising the scheme to buy congressional support for Silva's policies. The case is known in Brazil as mensalão, or big monthly allowance, for the sums of up to $10,000 handed over to politicians.

Silva faces no accusations of wrongdoing, and a Datafolha poll this year found that 57% of Brazilians wanted to see Silva return to the presidency in 2014.

Dirceu, a former revolutionary once seen as a potential president, was an early member of the leftist Workers party and served as party president from 1995 until 2002, when he was named Silva's chief of staff. The scandal broke in 2005 and forced him from the cabinet.

The public prosecutor's office said Dirceu had helped to orchestrate the flow of bribe money and broker deals with politicians. Dirceu denied involvement throughout the investigation.

His lawyers argued before the supreme court that the accusations were invalid, but did acknowledge some off-the-books accounting. They said Dirceu took responsibility for the irregular accounting and said Silva's administration had no knowledge of it.

Dirceu could face a sentence of two to 12 years in prison. Proceedings are continuing against a total of 37 defendants on 1,089 counts including corruption, money-laundering, misuse of public funds, embezzlement and conspiracy.

Other defendants include legislators and their business associates. Twenty-two have been convicted and four acquitted.

Dirceu entered politics as president of the leftist National Students Union and resisted Brazil's 1964-85 military dictatorship, which arrested him in 1968. The following year, an anti-regime group kidnapped the US ambassador Charles Elbrick and demanded the release of 15 imprisoned guerrillas, including Dirceu. Soon after arriving in Mexico he travelled to Cuba, where he had plastic surgery to change his looks and underwent guerrilla training.

Dirceu then sneaked back into Brazil and lived covertly, not even revealing his true identity to the woman he married. Only after the government decreed a political amnesty in 1979 did he go public, helping found the Workers party with Silva, then a leftist union leader.